Cohesive bonding with engineering thermoplastics such as ABS (acrylonitrile butadiene styrene copolymers), ABS/PC (acrylonitrile butadiene styrene copolymers/polycarbonate), PC (polycarbonate) and PMMA (polymethylmethacrylate) may be obtained by combining SEBS (polystyrene-poly(ethylene/butylene)-polystyrene) with polar thermoplastic elastomers such as TPE-E (thermoplastic polyester elastomers) or TPU (thermoplastic polyurethanes). Products of such kind are described for example in U.S. Pat. No. 5,149,589.
Thermoplastic elastomers containing SEBS/PP (polystyrene poly(ethylene/butylene) polystyrene/polypropylene) can exhibit outstanding cohesive bonding with polyolefinic substances such as polypropylene or a polyolefin. Even transparent materials with this composition are known. For example, Volume 1/2005, pages 34-36 of Kunststoffe includes an account to the effect that adhesion to PC, PMMA and MABS (methylmethacrylate acrylonitrile/butadiene styrene copolymers) is possible with materials containing S-SB-S (partially unsaturated styrene/butadiene block copolymer), which is sold under the brand name Styroflex®. This material has a hardness of 85 Shore A. This is considered to be too hard for many insulation applications, and it cannot be used in many outdoor applications because of the presence of double bonds.
Modifying SEBS with TPE-E or TPU and compatibilization using acid-modified SEBS or modified PP (polypropylene) can be expensive and difficult. In certain components, the multiphase construction can result in delamination in the area of the sprue gate. The materials must often be dried beforehand because they are blended with polar thermoplastic elastomers such as TPE-E or TPU that are prone to hydrolyzing. In addition, adhesion-modified materials according to the related art cannot be used as insulating materials at temperatures above 70° C.
Two fundamentally different methods are used in the related art to produce ornamental, partially electroplated parts or multicomponent parts with ornamental electroplating. In the first method, the hard plastic parts are injected, electroplated and extrusion coated with TPE. This method is used to manufacture side panels for electric shavers, for example. The disadvantage of this method is that it is expensive, because the tools and the process in general require extremely close tolerances. Moreover, the reject ratio associated with this method is not insignificant. Moreover, electroplating is a clearance-based process in which layer thicknesses are determined among other factors by the position on the electroplating jig. The variations in layer thicknesses inherent in the process must be controlled with sophisticated process guidance and monitoring systems. It is also considered a disadvantage that manual intervention is required in a high proportion of the various process steps. It is also disadvantageous that only a positive locking bond is created between the electroplated part and the soft plastic part, which means that no impermeability is created between the parts. If such a seal is necessary, it can only be produced with an even more complex equipment configuration and additional sealing elements. The second method takes into account a more complex part design, so that the number of process steps, as described in the first method, may be reduced and the equipment design may be simplified. Accordingly, the parts must be provided with a complicated sealing strip made from a non-electroplated plastic. This is necessary to prevent the electroplated layer from being damaged when the tool is closed. The disadvantage in this case is that a three-component injection molded part is needed, which entails greater investment.
There remains a need for methods of producing transparent polymer compounds with excellent cohesive bonding to amorphous engineering thermoplastics and good weathering properties, as well as a Shore hardness values below 70 Shore A. In addition, there remains a need for methods to electroplate hard/soft composite products selectively when standard commercial thermoplastic elastomers (TPEs) constitute the soft component.